08 seadoo challenger 1800 Cant rev over 5000 rpms

I have a sea doo challenger 1800 with twin 787s. The port engine is great revs to 7000 rpms smoothly no issues. The starbard will not rev past 5000 rpms in the water in drive. The rave valves have been cleaned, carbs rebuilt, new fuel filters, fresh gas and oil, and new spark plugs. Any suggestions? Also at idle afterthe boat has been run a while the port engine revs to 3500 than back down to 1500. Than the starbord revs to 3500 and back down. It does it a few times